Calculates the average price over the last 50 days.
200 day moving average is also used
They are theoretical resistance (stock moving up) and support levels (stock going down) used by many investors and automated tools in decision making whether to buy or sell a stock.
It is anticipated, but not guaranteed a stock will rise up to the 50 or 200 day moving average, whichever is lower.
Of course good or bad news changes the way the stock moves significantly.